A fluid dynamic bearing device is a bearing device that rotatably supports an shaft member in a non-contact manner by the action of dynamic pressure generated by a lubrication fluid in a bearing gap. High-speed rotation, high rotation precision, and low noise are the characteristic features of the fluid dynamic bearing device. Owing to these characteristics, it has been favorably used recently as the bearing device for motors mounted in information equipment and various other electrical equipment, more specifically, for the spindle motors of HDDs or other magnetic disk devices, CD-ROMs, CD-R/RWs, DVD-ROM/RAMS or other optical disk devices, MDs, MOs or other magnetic optical disk devices, for the polygon scanner motors of laser beam printers (LBP), and for fan motors.
FIG. 7 shows a known structure of a fluid dynamic bearing device incorporated in a spindle motor of a disk device or the like. The fluid dynamic bearing device 71 shown in the drawing includes a cylindrical housing 77 with an integral bottom, a bearing member or a bearing sleeve 78 secured to the inner circumference of the housing 77, and an shaft member 72 whose shaft part 72a is inserted into the bearing sleeve 78. Between the inner circumferential surface of the bearing sleeve 78 and the outer circumferential surface of the shaft part 72a are formed radial bearing gaps of radial bearing parts 73 and 74 at two, upper and lower, spaced-apart locations. First and second thrust bearing surfaces are provided respectively on both end faces of a flange part 72b at one end of the shaft part 72a. The first thrust bearing surface forms a thrust bearing gap (being a first thrust bearing gap) of a first thrust bearing part 75 between itself and one end face of the bearing sleeve 78, and the second thrust bearing surface forms a thrust bearing gap (being a second thrust bearing gap) of a second thrust bearing part 76 between itself and the inner bottom face of the housing 77.
With the fluid dynamic bearing device 71 having the above structure, axial positioning of the bearing sleeve 78 relative to the housing 77, i.e., setting of a predetermined gap dimension of the two thrust bearing gaps, is achieved for example in the following manner: The shaft member 72 and the bearing sleeve 78 are set inside the housing 77 such that the sum of both thrust bearing gaps is zero; the shaft member 72 is then moved towards the opening side of the housing 77 by a distance that is equal to the sum of both thrust bearing gaps; finally, the bearing sleeve 78 is secured to the housing 77 (see, for example, Patent Document 1).    [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-239974